Tea leaves are extracted in warm or hot water, and the obtained extract is contacted with a cation exchange resin ionically bonded to potassium ion. The potassium ion is ionically bonded to the cation exchange resin in advance. Divalent ions in the tea beverage are replaced with the potassium ions from the cation exchange resin. The electrical conductivity of the extract is controlled in this whole process. The natural flavor and quality of the tea are thereby maintained more certainly, since metal ions that cause muddiness or precipitation are effectively removed.